The present invention relates generally to vibratory material-screening apparatus used in classifying solid particulate matter and, more particularly, to a vibratory screen tensioning assembly for use in such apparatus.
Vibrating screening decks have been widely used in the past for the classification and separation of particulate solids of varying particle sizes and compositions, such as limestone, coal and other ores. Such screening decks have typically comprised a generally rectangular frame which is suspended in operation and which has one or more screen cloth decks in the frame upon which the materials to be classified are deposited. The frame and screens in such decks are suspended at a angle and the entire frame with its screens is vibrated to cause the solid particulates to move down the screens. As the materials move down the vibrating screen, solids of smaller mesh size pass through the screen as "unders" and solids of larger dimensions are discharged from the lower end of the screen as "overs".
In U.S. Pat. No. 4,444,656 an improved vibrating screening deck assembly is disclosed in which one or more wire cloth screens having a preselected mesh size to allow the passage therethrough of material are anchored at opposite ends to spaced members extending transverse to the frame walls. In such assembly one end of the screen is anchored and the screen is stretched across one or more tappet assemblies that also span the width of the frame and the other end of the screen is anchored at its opposite end. The tappet assemblies underlie the screen to impart vibration directly to the screen, rather than to the frame, and the tappet assemblies support the screen. To achieve optimum operation of the classifying apparatus the screens must be tensioned uniformly to provide a uniform screening surface. Therefore, the screens in such assemblies perferably should include some sort of means for tensioning the screen over the tappet assemblies.
In U.S. Pat. No. 4,444,656 such tensioning is accomplished by a tensioning plate having a width substantially equal to that of the screen. The plate has a hooked flange that engages a similar hooked flange on the screen ends and a plurality of tensioning bolts by which the screen tension is adjusted by turning individual bolts laterally spaced across the screen.
Although the last mentioned tensioning arrangement is capable of satisfactory adjustment of the screen tension, it suffers several shortcomings. One such shortcoming is that the tension that can be imparted to the screen deck is limited by the length of the tensioning bolts. Additionally, the adjustment of all of the bolts must be uniform to ensure that a uniform tension is applied to the screen and each of the bolts must be individually adjusted which is time consuming and usually requires that the assembly be placed out of operation. The foregoing shortcomings are compounded, where multiple screen decks are employed. Moreover, the need to place the assembly out of operation during adjustment is, itself, disadvantageous because adjustment would be faster and more accurate if it was accomplished during operation so the effects of adjustment could be instantaneously observed during operation.
The tensioning assembly of the present invention overcomes the aforementioned shortcomings. In a tensioning assembly incorporating the principles of the present invention, screen tension adjustment may be accomplished rapidly and uniformly and without the need to place the assembly out of operation. Moreover, such adjustment may be accomplished over a wide range of adjustments. Additionally, where multiple screens are present, they can be tensioned simultaneously so that each individual screen receives an equal amount of tension and total adjustment time is reduced.
In one principal aspect of the present invention, a classifying apparatus includes a rigid frame, at least one classifying screen in the frame, and means for tensioning the screen. The improvement in the means for tensioning the screen comprises means for stationarily anchoring one end of the screen and elongate rotatable mean adjacent the other end of the screen and extending across the width of the screen and the frame. The rotatable means includes engaging means for engaging the other end of the screen substantially across the width of the screen. Mounting means for mounting the elongate rotatable means for rotation relative to the frame is provided along with means for rotating the rotatable means to draw a tension on the screen when the screen is anchored at one end and engaged at its other end by the engaging means.
In another principal aspect of the present invention, the aforementioned apparatus includes a pair of screens in the frame and means for stationarily anchoring one end of each of the screens. Elongate rotatable means, one for each screen, are positioned adjacent the other end of each of the screens and extend across the width of the screens and the frame. The rotatable means include engaging means for engaging the other end of the respective screens substantially across the width of the screens. Mounting means for mounting the elongate rotatable means for rotation relative to the frame and means for rotating the rotatable means to draw a tension on each of the screens when said screens are anchored at their one end and engaged at their other end by the engaging means are provided.
In still another principal aspect of the present invention, the aforementioned rotatable means extend beyond and to the side of the frame opposite the screens, and the means for rotating the rotatable means are also on the last mentioned side.
In still another principal aspect of the present invention, the aforementioned means for rotating the rotatable means comprises a lever on each of the rotatable means.
In still another principal aspect of the present invention, the aforementioned means for rotating the rotatable means includes a tensioning cable attached between the levers, and tensioning means on the cable for selectively tensioning the cable, whereby both of the rotatable means are rotated simultaneously and the screens are simultaneously tensioned.
In still another principal aspect of the present invention, the apparatus includes a pair of cables, one on each side of the frame.
In still another principal aspect of the present invention, the aforementioned ends of the screens are releasably anchored and engaged, respectively.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.